The paper in question is a review of 20 years of existing research into the health effects of marijuana use. By design, it doesn’t tell us anything we don’t already know. The focus is almost exclusively on the effects of long-term heavy (daily or near-daily) marijuana use: “this paper deals with the adverse effects of cannabis smoking, especially the adverse health effects of regular, typically daily, cannabis smoking,” the author, Wayne Hall, a drug adviser to the World Health Organization, writes.